The background description provided herein is for the purpose of generally presenting the context of the disclosure. Work of the presently named inventors, to the extent it is described in this background section, as well as aspects of the description that may not otherwise qualify as prior art at the time of filing, are neither expressly nor impliedly admitted as prior art against the present disclosure.
Active Fuel Management™ (AFM) or variable displacement allows displacement of an internal combustion engine (ICE) to change by deactivation of one or more cylinders. Deactivation of cylinder(s) improves fuel economy of a vehicle. During light-load conditions, an AFM mode may be enabled to deactivate cylinders of an engine. The deactivated cylinders may be reactivated during heavy-load conditions. As an example, during an AFM mode, activated cylinders on a V8 engine may be reduced to 4. As another example, during an AFM mode, activated cylinders on a V6 engine may be reduced to 3.
During an AFM mode, fuel is not provided to deactivated cylinders. Also, intake and exhaust valves of the deactivated cylinders are maintained in a closed state. This prevents air and fuel from entering the combustion chambers of the deactivated cylinders and prevents contents of the combustion chambers from exiting the deactivated cylinders. The deactivated cylinders perform as air shocks during the AFM mode.
Since the exhaust valves of the deactivated cylinders do not open during the AFM mode, oil on the cylinder walls can build up in the combustion chambers. Although pistons in the cylinders include oil rings that are used to prevent oil from entering the combustion chambers, the oil rings do not completely remove all of the oil on the cylinder walls. This oil may form a mist in the combustion chambers and build up over multiple combustion cycles.
The oil can build up, for example, between electrodes of spark plugs. Since oil performs as an insulator, spark that is created by a spark plug may jump between a first electrode (e.g. side electrode) and an insulator (e.g. ceramic material) surrounding a second electrode (e.g. center electrode) of the spark plug. This causes holes in the insulator on the second electrode and results in abrasive debris in a combustion chamber, which can scratch cylinder walls. The debris can cause premature piston ring and cylinder bore wear, which can lead to increased oil consumption.